In data storage drives, user data is stored on tracks of storage media. A transducer or probe is positioned to move along a track to write and read user data on the storage media. In addition to the user data, position data is also provided on the storage media.
The position data can include servo marks that, when read, generally indicates position coordinates (e.g., X, Y coordinates, or track number, cylinder number, sector number) of the transducer or probe relative to the media surface. Position data can also include preambles that indicate local alignment between a track and the transducer or probe; A wide variety of formats for servo marks and preambles are known. With areal densities available in conventional magnetic storage drives, lithographic techniques (which include deposits of radiation sensitive layers), have adequate resolution to effectively define servo marks on the magnetic media.
The data storage drive includes a servo system (feedback system) that positions the transducer or probe over a selected track based on feedback of the position data. The servo system typically has a “seek mode” that moves the transducer or probe from one track to another track based on reading servo marks. The servo system also typically has a “tracking mode” in which the transducer or probe is precisely aligned with a selected track based reading on preamble data.
At the time of manufacture of a magnetic data storage drive, the servo marks are positioned on the storage media. During operational use of the data storage drive, the servo marks are read by the transducer or probe, but there is typically no need to erase and rewrite servo data during operation. The position of conventional magnetic servo sector data on the media is therefore stable and does not creep significantly during the operational life of the data storage drive.
There is a desire to increase the storage capacity of data storage media and also a desire to reduce the size and weight of data storage media on new designs. This leads to a need for increased areal density for the data storage media that can't be met with conventional storage technologies.
Scanning probe storage based on ferroelectric media (FeProbe) can be used to provide the increased areal density. There are, however, new problems that arise with the increased areal density and with FeProbe itself that are not present in earlier storage devices.
In particular, there is a desire to increase areal densities to a level where servo marks have length scales on the order of only several tens of nanometers. It is not practical to define servo marks at this small length scale using conventional lithographic capabilities, and other methods must be found to provide servo marks.
Servo marks (or other position data) can be polarized on the ferroelectric memory itself at this small length scale, however, the characteristics of FeProbe do not permit stable positioning of servo sector data. When data is read from FeProbe with a probe, the conventional process of reading the data inherently erases (removes) the data from the FeProbe. An electronic circuit that provides the read operation of FeProbe data must follow up and automatically provide a subsequent write operation of the same FeProbe data in order to avoid loss of the data on the ferroelectric media. This is not an insurmountable problem for user data. With position data (e.g., servo marks), however, the repeated reading and automatic rewriting of position marks will inevitably lead to creep of the positions of the position marks and loss of accurate position information. This instability or loss of accurate position information limits the useful life of the FeProbe device. Adjacent FeProbe tracks with user data will become misaligned due to position creep of position data. User data tracks will eventually overwrite or interfere with one another.
A method and apparatus are needed to provide FeProbe with position data that has locations on the ferroelectric media that are adequately stable. There is a desire to provide position data that can be conveniently read with the same probe and electronics that are used to read user data. There is also a desire to provide position data that can't be erased by the probe and electronics used to read user data, and which provides an electronic signal as similar as possible to the user data. Aspects of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.